Vitreous enamel opacification and process



Patented June 28, 1949' IVITREOU S "ENAMEL OPAGIFICATIDN! PROCESS fifflemyb'es'terle and Riibert' A-.-=oeaeae,

Bellei'lllefi lll. ""No Drawing. IApplication July 12, 1946, serial N0. 683,158

imhisimventlcn relates 'to cp2 rciil'ers 'ior porcez-liaim enamlstand more specincallyi to opae'iflcatidn lcfrazirconium frits by the 1156 61 ila/willed aluniiiia -"as a mill iaddition ornateiiler. We haveShow iiiscovereii that by' the mse of from /g% to i8% ba*sed* upon the weiglit of the frit of al r' iliauiflumin'aeas a mill addition for opaci fication of vitreous enamels of the zirconium type we are able to improve the whiteness of such enamels. 'I1'lis- 'ffectwas"not to be exape'cted rinasmueheas aluminawhas' no "Whitening effect as a mill addition in mostrporcelain 'ena-mels. Theresultis that improved opacity is attained by the "use of a"relativel'y"'very cheap material as compared tto dprevious opaquin'g i' agents.

fBy zirconiumttype enamel we mean those-made from frits now .being .sold-incommercial quantitles and knownflfithe tradeaszlrconium frits,

as welllas similar compositions. These frits are ti'ilraracterizedmby rthe use inittheir formulae of .iflatively large .quantities (of ilzirconium oxykiompounds .usuallytin .theltirorm-fiof the mineral zircon as well as alkali, Silica, alumina, boric oxide, fluorine and optionally minor constituents such as alkaline earths, zinc oxide, lead oxide, phosphorus, magnesia, etc. Some sample compositions (theoretical melted) are shown in Table I.

Table I Zirconium frit formulae are devised with great attention to detail and vary over a wide range of proportions, essentially they contain about 20% to 50% of SiOz, 5% to 20% 2102, 5% to B203, 5% to A1203 and 5% to 20% F2. Other ingredients are optional and impart various properties which are desirable but not absolutely necessary. Frit batches so constituted are smelted and quenched and mixed at the mill with various usual materials such as electrolyte, suspending tmfiilaims. (Cl. 10648) :1 same?! n a Crystal-mamas shownkby l X-ray'linalysis Tempei-atura-Eeii ngrue Calcination at 1000 C. for 5 to 10 hours or more will give a useful product but we prefer to heat above 1200 C. for one hour or more and best results are had by heating at 1800 C. for an hour or more. Heating may be in an atmosphere of air or other non-reducing atmosphere. Using 2% of alumina calcined at various temperatures in the same frit and keeping all conditions comparable except the time of calcination of the alumina resulted in enamels having the following reflectances:

(1) A1203 calcined at 600 C., reflectance 69.9, (2) A1203 calcined at 900 C., reflectance 70.0, (3) A1203 calcined at 1100" C., reflectance 70.2, (4) A1203 calcined at 1200 0., reflectance 70.5, (5) A1203 calcined at 1800 C., reflectance 70.6.

While these data do not show a smoothly rising curve, they do show a definite improvement in the region of 1000 C.-1200 C. and "we have found that heating for 5 hours at 1000? C. will give definite improvement consistently as well as heating at 1200 C. "to 1800 C. for 1 hour or more.

The use of alpha alumina as a mill addition opacifler was tried out in-five different commercial frits, one from each of five commercial producers of zirconium type frits (exact compositions unknown to :us but definitely similar to the compositions of Table I). In all cases a definite 3 whitening effect was obtained. In frits of the antimony type no improvement was noted. While alpha alumina did not give greater whiteness Table III which is based upon a series of tests using varying amounts as mill addition and measuring the reflectance of the resulting enamels, the rate of application being 40 gm. per sq. ft. in all cases'and other conditions being identical.

Table III Per Cent Alpha $5 5 3 y fi l i fii 1g a the Mill 1m 0. 5 73.1 1 7a. 5 :2 7s; 9 4 74. 2 8 74:6

The use of alphaalumina at the mill is advantageous not only in its opaquing eiTect as indicated but also in that -it gives a more nearly uniform opacity, clouding very small transparencies which are visible to the eye but, do'not show up in the total reflectance as measured by the refiectometer. It is possible to obtain somewhat improved opacity by the use of alumina which has been only partially converted to the .alpha form, however such material is not as good as that which has been completely or nearly completely converted to the alpha form.

This application is a continuation-in-part of our application, Serial No. 611,256, filed August 17, 1945, now abandoned.

Having thus described our invention, what we claim is:

1. In a process of making a vitreous enamel, the step of milling a zirconium type frit comprising 20% to SiOz, 5% to 20% zrOz, to 15% B203, 5% to 20% A1203 and 5% to 20% F2, percentages being by. weight, together with from %%;to 8% of the weight of said frit of alpha alumina.

2. A vitreous enamel composition essentially consisting of a zirconium type frit, and a mill addition opacifier, said frit comprising from 20% to 50% SiOz, 5% to 20% ZrOz, 5% to 15% B203, 5% to 20% A1203, and 5% to 20% F2, and said mill addition opacifier being alpha alumina in proportion of from /g% to 8% of the frit, by weight.-

3. A vitreous enamel composition essentially consisting of a zirconium silicate containing frit and from /'2% to 8% of the frit, by weight, of alpha alumina, said frit on a theoretical melted composition basis comprising ZrOz 11 to 14.8 parts by weight, S102 25.3 to 48 parts by weight, B203 7 to 13.7 parts by'weight, A1203 7 to 10 parts by Weight, NazO plus K20 13 to 17 parts by weight, and F2 from 2 to 12 parts by Weight.

' HENRY OESTERLE.

ROBERT A. OE'STERLE.

file of this patent:

UNITED STATES PATENTS Number Name Date 1,104,286 Mayer et al July 21, 1914 I 2,347,187 Frost 1 Ap 1944 FOREIGN PATENTS Number Country Date 70,217" Austria 1915 5,790 Holland 19 1 705,665

Germany 1941 

